1. Field of the Invention
The present invention relates to an optical recording/reproducing device having a means for preventing overwriting of data in a recording medium.
2. Description of the Related Art
Recently, a great deal of attention has been paid to an optical recording/reproducing device which can record data in a recording medium at high density or can reproduce data, which is recorded in a recording medium at high density, at high speed, by radiating a light beam.
In the above device, since data is recorded at high density, a light beam must be focused to be sufficiently small for recording and reproduction. For this reason, recording and reproduction are performed by performing focusing control of an objective lens for focusing a light beam on a recording medium while performing tracking control for causing the light beam to follow a current track.
A recording medium utilizing phase change is available.
When data is read from an optical disk utilizing phase change by read power, since the read power is low-level optical power, the optical disk is kept in an amorphous state and has a low reflectivity (or a reflection amount is small). However, if a light beam having high-level write power is radiated onto the optical disk, the amorphous state is phase-changed into crystalline state, and the reflectivity is increased.
Binary data, therefore, can be recorded in such an optical disk by utilizing a difference between these reflection amount levels.
The optical disk utilizing the above-described phase change is of a write-once type in which data can be written in an addition manner. Similar to optical disks of other types, in this write-once type optical disk, when data is written in a data area allowing data to be written therein, overwriting of data in the data area must be prevented. However, a means for efficiently preventing overwriting has not been developed.